Enhancing Shielding Efficiency of Separate Shell Magnetic Shield Using Two Independent Controllers

A new strategy using two independent controllers to cancel both static and time varying magnetic fields is introduced. Two sets of coils are utilized for active compensation in the
$y$
-direction. The system shielding efficiency improved to 800 at 30 Hz from 20 in the case of passive shield only. The performance of the shield is further investigated by optimally selecting the relative position between the feedback and measuring sensors. Also, the distribution of
$y$
-component of magnetic field inside the shell along
$x$
-direction under different shell separation is investigated. The results show that the new controller was able to reduce the noise at 1 Hz to 20
${\rm pT}/\surd{\rm Hz}$
, and the noise at 60 Hz is reduced more than
$100\times$
, with a noise floor of 3
${\rm pT}/\surd{\rm Hz}$
.